1. Field of the Invention
The present invention relates to an improved process for the preparation of polyisocyanurate-polyisocyanates, by partial catalytic cyclotrimerization of polyisocyanates, the subject reaction ultimately and deliberately being stopped or terminated when the trimer content reaches the predetermined and desired value. More especially, the present invention essentially relates to an improved process for deactivating the catalyst employed therein, said catalyst comprising an aminosilyl compound.
2. Description of the Prior Art
In my U.S. Pat. No. 4,412,073, assigned to the assignee hereof, a process is described for the preparation of monomeric or polymeric compounds containing isocyanurate groups, and especially of polyisocyanurate-polyisocyanates, by catalytic cyclotrimerization of aliphatic or alicyclic isocyanates in the presence of catalytically effective amounts of compounds containing one or more aminosilyl group(s). More particularly, said '073 patent describes a process for preparing polyisocyanurate-polyisocyanates by partial catalytic cyclotrimerization of polyisocyanates, especially of aliphatic or alicyclic diisocyanates; in this case, the cyclotrimerization reaction is stopped when the isocyanurate group content reaches the required value, by deactivating the aminosilylated catalyst. Various means for deactivating the catalyst have been proposed. Thus, in the aforesaid '073 patent such catalyst deactivation results via the destruction thereof by means of an acidic compound (hydrochloric acid, acid chloride) which is added to the reaction mixture. And in my U.S. Pat. No. 4,537,961, also assigned to the assignee hereof, the catalyst is destroyed or consumed by the addition of an organic compound containing at least one hydroxyl group to the reaction medium, such as enols, alcohols, phenols, oximes, or compounds containing one or more hydroxysilyl group(s), or of a compound produced by the reaction of a hydroxylated compound of this type with a reactant containing one or more isocyanate group(s), such as carbamates, which may be produced in situ by the reaction of a hydroxylated compound with excess diisocyanate, under conditions employed for the addition of the hydroxylated compound. After the reaction has been stopped, the excess diisocyanate is separated from the polyisocyanuratepolyisocyanate by distillation.
It has, however, been found that, during storage, the products obtained in this manner can sometimes give rise to free diisocyanates, which interfere with the use of the polyisocyanurate-polyisocyanates in coating compositions and especially in varnishes.